How do I get the bung out of the top of the water tank in order to fit the immersion heater? It appears to have been put in with some kind of plumbers paste and I am worried I might damage the tank if using too much force.

Edwardfrank,
Partly drain down the tank say to 3/4 full, heat the bung with a blowtorch and use a box spanner to try undoing the bung. There's a good chance you will ruin the tank - depends how old the plumbers mate is.
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